1. Field of the Invention
The invention concerns a printing apparatus of the type having a separate contact pressure element for franking strips. Such a printing apparatus has a removable, box-shaped module at the lower part of a housing and a transport device with a transport belt in the upper part of a housing, wherein mail pieces are transported in a gap between the two parts. The printing apparatus is connected with mail processing apparatuses, in particular for use in a franking machine.
2. Description of the Prior Art
As used herein, a mail piece is a printing substrate such as a letter or a small width, elongated length printing substrate such as franking strips, or another flat good that has three dimensions and that is suitable for receiving print indicia.
A printing apparatus of modular design with a removable, box-shaped module is known from German Utility Patent DE 202010015354 U1, in which contact pressure elements are provided in order to press a flat item onto a transport belt from below (FIGS. 1a and 1b).
From German Utility Patent DE 20201001535101, a device is known to lower, position and raise contact pressure elements of a printing apparatus. This has two guide channels, a rocker and connection elements, as well as shaped parts, and, together with the box-shaped module in the lower part of the franking machine, can be completely removed from the franking machine at the front in order to facilitate or accelerate a dust cleaning. The rocker must be operated to lower the contact pressure device and before a removal of the box-shaped module. The guide channels and the remaining aforementioned components interact with two guide elements that project from the lower part of the printing apparatus. Due to a contour of the guide elements, during the sliding of the box-shaped module into the printing apparatus the contact pressure device is initially moved counter to the z-direction (i.e. downwardly) and then in the z-direction (i.e. upwardly) upon reaching a predetermined feed position.
German Utility Patent DE 202011109208 U1 discloses a printing apparatus wherein a brush body is mechanically coupled with a spring system that has a number of spring elements that are arranged between a base plate and a ground plate. The spring elements are compression springs with a spring constant that is so small that the brush body placed on the base plate is deflected counter to the elastic force of the spring elements in the event that a very thin flat item is transported further via the transport belt. The compression springs of the contact pressure device are pre-tensioned to a minimum contact pressure force of F2min, which is just sufficient in order to transport thin flat items such as franking strips without the brush elements of the brush being deformed. Due to the small spring constant of the compression springs, the deflection thereby takes place before the brush elements of the brush can yield. The spring force increases linearly with the thickness of the flat item, up to a value F2max. Only then at the spring force F2max=F1min are the brush elements effective because the resilience of the spring elements is limited to F2max. The spring force of the brush elements increases exponentially with the thickness of the flat item up to a value F1opt. Given a thick item (such as letters of 3 mm) an additional spring system is active that is arranged below the first spring system between the ground plate and a floor plate of the housing. The spring elements of the additional spring system are likewise compression springs, but with a spring constant that is larger than that of the compression springs of the first spring system, such that at F1opt=F3min, the brush elements for the deflection of the brush body are increasingly ineffective counter to the spring force, because the resilience due to the spring elements of the additional spring system is transitioned into a force range as of F3min. The spring force now additionally increases linearly with the thickness of the flat item up to a value of F3max. This solution has been optimized for thick flat goods and for a long service life of the brush. However, a disadvantage can occur in the event that a very thin flat good (such as a franking strip) should be transported further via the transport belt. Then the force effect F2max must be adjusted in an incremented dosed manner (which is complicated) so that a slippage at the transport belt is avoided in the transport of the franking strip.
In German Utility Patent DE 202011108254 U1 an arrangement is proposed for printing on strip-shaped printing substrates. The printing substrates are transported in a direction designated as the x-direction of a Cartesian coordinate system by a known transport module with a tensioned transport belt revolving by being driven by rollers, and with a counter-pressure device with elastic, elastically arranged contact pressure elements, the printing substrates are printed by a print head located behind a printing window. A module with a magazine for strip-shaped printing substrate is arranged in the entrance region for the printing substrate and in the engagement region of the transport belt. The transport belt of the transport module simultaneously serves as a pull-off device. Each strip-shaped printing substrate has a border region and a printing region, with the border region amounting to at least one third of the printing region width. The module with the magazine is arranged laterally offset from the transport belt (see FIG. 2) so that the printing substrates are engaged by the transport belt only in the border region, and are wider by the amount this border region than the width that would otherwise typically be the widest strip-shaped printing substrate. The transport belt runs outside of and next to the printing window, and the printing substrate with the remaining region to be printed is directed by the transport belt below the printing window. A transport module lies on a lateral letter run guide, and opposite this is situated a counter-pressure device, wherein a printing substrate is transported further while clamped between the aforementioned two means during the printing. A disadvantage of this solution is the engagement of a strip-shaped printing substrate (franking strip) only in the border region, wherein a printing takes place in a wider printing region of the strip-shaped printing substrate. This is solved in precisely the reverse manner for other (normal) printing substrates such as letters. A franking imprint is printed in a narrow (approximately 1 inch) border region of the letter that is predetermined by the postal authority, while the letter is engaged in a remaining region that is wider than the border region. By interaction with the adjustably set force effect of the spring force in the range F2min to F2max, the narrower border region of the franking strip can have a disadvantageous effect on the setting of a slip-free transport, so that an offset of the imprint appears in the print image.
The printing apparatus is equipped with an ink printing device on which a flat item is pressed in a known manner by means of a contact pressure device. The ink printing device has exchangeable ink cartridges and a print head, and the contact pressure device is a component of a box-shaped module that is removable and can be inserted in an insertion direction y. The contact pressure device is charged with a spring force in order to press the flat item onto a transport belt in the contact pressure direction z. A sensor for triggering printing by the ink printing device is arranged in the transport path. During transport in the transport direction x along the transport path, the flat item is printed by the ink printing device.